1. Field of the Invention
The present invention relates to an electrostatic chuck and a method for manufacturing the same.
2. Description of the Related Art
In semiconductor or liquid crystal device manufacturing processes, electrostatic chucks have been used to adsorb and hold semiconductor substrates, glass substrates, or the like. Such electrostatic chucks include Coulomb force type chucks to adsorb substrates and Johnson-Rahbeck force type chuck to adsorb substrates. A Coulomb force is an electrostatic adsorption force generated between the electrode of an electrostatic chuck and a substrate placed on the surface of the dielectric layer of the electrostatic chuck. When an electrostatic chuck uses the Coulomb force to adsorb a substrate, the resistivity is required to be at a high level over the operating temperature range in order to provide appropriate substrate-releasing performance.
Alumina, which has high volume resistivity at room temperature and is inexpensive is generally used for electrostatic chucks that utilize a Coulomb force to adsorb substrates (see for example Japanese published Patent Application (JP-A) No. 09-283607)
In recent years, however, the temperature of the environment to which electrostatic chucks are exposed in semiconductor equipment has tended to increase. For example, electrostatic chucks have been used in the process of heating substrates in chemical vapor deposition (CVD) systems or the like or subjecting substrates to high-performance plasma treatment under a high heat input environment in etching systems or physical vapor deposition (PVD) systems to provide films of additional component materials, etching, and the like. Under these circumstances, electrostatic chucks have been required to have high thermal conductivity to improve thermal uniformity and/or efficiently transfer heat from substrates.
The thermal conductivity of alumina is at most 30 W/mK, which is relatively low. Therefore, electrostatic chucks having a base part made of alumina have a problem of insufficient heat transfer from substrates. Thus, the present inventors have proposed an electrostatic chuck that has a high level of volume resistivity and thermal conductivity when using Coulomb force in a high-temperature environment and also proposed a method for manufacturing such a chuck (see for example JP-A No. 2006-269826).
In general, Coulomb force-type electrostatic chucks are required to have the characteristics described below. However, the operating temperature of Coulomb force-type alumina electrostatic chucks has an upper limit of 200° C. In addition, alumina has a thermal conductivity of about 30 W/mk, and, therefore, it is difficult to provide a high level of thermal uniformity with alumina.
(1) Volume resistivity at room temperature and applied voltage of 2000 V: 1×1016 Ω·cm or more
(2) Volume resistivity at the upper limit of the operating temperature and applied voltage of 2000 V: 1×1016 Ω·cm or more
(3) Adsorption force: 20 Torr (2666 Pa) or more (at room temperature (RT) to the upper limit of the operating temperature)